In the oil and gas producing industry there is a long-established need for generation electrical power inside a wellbore, particularly a wellbore in the state of producing hydrocarbon fluids.
Whilst many possible solutions to the problem have been suggested, the industry is presently using battery packs and cable connection to the surface.
Among the technical solutions unsuccessfully proposed is the use of thermocouples integrated in or attached to the wall of tubes in the wellbore.
For example, in the U.S. Pat. No. 6,150,601 there is described a method and apparatus for generating electrical power downhole by applying a temperature gradient across a at least two thermocouples. In the U.S. Pat. No. 6,380,476 a thermocouple is placed inside a side-pocket mandrel and brought into contact either to the inner wall of the casing of a wellbore or the formation. In the U.S. Pat. No. 5,929,372 which relates to underwater pipe and not to a wellbore there is suggested to use a stack of high-temperature bismuth telluride thermocouples heated by the wellbore fluid from within and seawater from the outside to maintain a sufficient temperature gradient across the thermocouples.
In the light of the know state of the art, it is clear that an applicable thermoelectric generator requires for further improvements to be operable at a downhole location. It is therefore seen as an object of the present invention to provide an apparatus and method for generate electrical power using the thermo-electrical effect with increased efficiency.